Automata, Languages and Programming

Volume 3580 of the series Lecture Notes in Computer Science pp 803-815

Single-Database Private Information Retrieval with Constant Communication Rate

  • Craig GentryAffiliated withDoCoMo Communications Laboratories USA, Inc
  • , Zulfikar RamzanAffiliated withDoCoMo Communications Laboratories USA, Inc

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We present a single-database private information retrieval (PIR) scheme with communication complexity \({\mathcal O}(k+d)\), where k ≥ log n is a security parameter that depends on the database size n and d is the bit-length of the retrieved database block. This communication complexity is better asymptotically than previous single-database PIR schemes. The scheme also gives improved performance for practical parameter settings whether the user is retrieving a single bit or very large blocks. For large blocks, our scheme achieves a constant “rate” (e.g., 0.2), even when the user-side communication is very low (e.g., two 1024-bit numbers). Our scheme and security analysis is presented using general groups with hidden smooth subgroups; the scheme can be instantiated using composite moduli, in which case the security of our scheme is based on a simple variant of the “Φ-hiding” assumption by Cachin, Micali and Stadler [2].